Sabine Lisicki staved off three match points before battling into the last four at the BNP Paribas Open on Thursday, the German edging out defending champion Flavia Pennetta 6-4 6-7(3) 7-6(4) in an enthralling contest.
The 24th seed advances to face Jelena Jankovic in the semi-finals on Friday after the Serb progressed when Ukrainian qualifier Lesia Tsurenko retired from their last eight encounter with an ankle injury while trailing 6-1 4-1.
Lisicki nearly sealed a straight sets win when she earned her first match point while holding a 5-4 advantage in the second before the Italian produced a magical shot to spark a rally that leveled the match.
Pennetta then forged three match points of her own at 5-4 in the decider before Lisicki fought back to claim victory in a tiebreaker.
"It's unbelievable," Lisicki said in a courtside interview.
"It's such a great feeling to be part of such a great match. She saved a match point with an unbelievable backhand. I could not have done much different there and then I saved three match points in the third set.
"It was just an unbelievable feeling to play in front of all of you," she added for the fans.
Former champion Jankovic, meanwhile, broke an error-prone Tsurenko twice to breeze through the opening set in 22 minutes and twice more in the second before the Ukrainian walked across to her opponent and told her the match was over.
"It's never nice to end a match in that way," Serb Jankovic, 30, said on another hot day at the Indian Wells Tennis Garden. "In the second set, she started limping and I saw that she had some problem."
"I had to just focus on my game and try to make as many balls as possible in the point. I was feeling pretty good out there. I was playing my game and waiting for my chances to execute. I was solid."
"I'm really sorry she got injured. She has had such a great tournament, she has beaten a lot of great players in the draw. Unfortunately she couldn't play a great match today."
Tsurenko, ranked 85th in the world, injured her right ankle during her upset of sixth-seeded Canadian Eugenie Bouchard in the previous round and was noticeably restricted in her movement against Jankovic.
She failed to hold serve in the second and sixth games of the match to be swept aside in the opening set before calling for her trainer to re-tape her ankle.
Tsurenko, who double-faulted five times during the curtailed match, was again broken in the first and fifth games of the second set before she retired.
The other semi-final will be contested by Romanian Simona Halep and top seed Serena Williams, back at Indian Wells after a 14-year boycott of the event where she alleged she had suffered racist abuse from fans.
American Williams, who clinched her 19th grand slam singles title at this year's Australian Open, and world number three Halep both advanced from the quarters on Wednesday.